1. Field of the Invention
The present invention relates to a Fresnel lens sheet, and also to a transmission-type projection screen which utilizes the Fresnel lens sheet.
2. Description of the Related Art
A Fresnel lens sheet and a transmission-type projection screen are generally used in order that projection light incident on an incident surface is polarized and emitted from an light-emission surface at a desired angle.
However, a portion of the projected light is reflected at the light-emission surface and eventually emitted from a position which is slightly dislocated from the position where the light should be emitted, resulting in generation of a what is called double image.
FIGS. 11 and 12 are drawings which show an optical path of light which is incident on a conventional Fresnel lens sheet 100 or 101.
Most of an incident light Lin which is incident on the Fresnel lens sheet 100 of FIG. 11 is emitted from a light-emission surface 100b as a normal emission light Lout. However, a portion of the incident light Lin is reflected back at the light-emission surface 100b, entirely reflected at an incident surface 100a and becomes a disoriented light Lout100. Since the disoriented light Lout100 is emitted from a position which is distanced from the normal emission light Lout, the resulting image is observed as a double image.
Further, an incident light LAin which is incident on the incident surface 101a of the Fresnel lens sheet 101 of FIG. 12 is emitted from a light-emission surface 101c as a normal emission light LAout101. However, an incident light LBin which is incident on an ineffective surface 101b is reflected back at a light-emission surface 101c, subjected to inner surface reflection and becomes a disoriented light LBout101. Since the disoriented light LBout101 is emitted from a position which is distanced from the normal emission light LAout101, the resulting image is observed as a double image.
Therefore, the Fresnel lens sheet 100 or 101 is conventionally made thin so that the length of the optical path of the light reflected back at the light-emission surface 100b or 101c is shortened, in order that the distance between the position where the emission light Lout is emitted and the position where the disoriented light Lout100 is emitted, as well as the distance between the position where the emission light LAout101 is emitted and the position where the disoriented light LBout101 is emitted, are made closer. By such modification, the double image can be made less conspicuous as compared with the unmodified Fresnel lens sheet.
However, in the conventional Fresnel lens sheet as described above, as the thickness thereof is made thin, there arises a problem that the Fresnel lens sheet exhibits poor self-supporting property and cannot be held easily when the Fresnel lens sheet is used for a screen of large-size.
Examples of a method of holding a thin Fresnel lens sheet include a method of applying tension to a Fresnel lens sheet. However, this method has drawbacks in that the method requires provision of specific members for applying tension to a Fresnel lens sheet and that the size of the portion thereof other than the display of the back-projection-type screen increases, which results in an increase in the production cost.
Further, there also arises a problem that the holding frame for holding the Fresnel lens sheet must have a width of several tens of mm. In a multi-display device which effects multi-displaying faces or an enlarged displaying face by stacking up a plurality of transmission-type (or a back-projection-type in other word) projection screens, especially, there arises a problem that connection portions having a width of tens of mm, at which image cannot be displayed, are inevitably generated between the displays because the width of the holding frame cannot be reduced any further.
An object of the present invention is to provide a Fresnel lens sheet and a transmission-type projection screen which can be easily held and exhibits less conspicuous double image as compared with the conventional Fresnel lens sheet.
The present invention solves the above-mentioned problems by means for solution as described below. Although the embodiments of the present invention are described with corresponding reference numerals attached thereto, these reference numerals by no means restrict the present invention.
Specifically, a first aspect of the present invention provides a Fresnel lens sheet (10, 20, 30, 40, 50) for polarizing and emitting projection light, comprising: a lens layer (11, 21, 31, 41, 51) at which Fresnel lens configuration has been formed; a base material layer (12, 22, 32, 42, 52) provided further toward a light-incident or light-emission side than the lens layer; and a total reflection surface (11a, 23a, 31a, 40a, 50a) for totally reflecting a portion of the projection light, wherein the total reflection surface is disposed between an incident surface (12a, 22a, 32a, 41a, 51a) and a light-emission surface.
In the first aspect of the Fresnel lens sheet (10, 20, 30, 40, 50), a disoriented light originated from a part of the projection light incident on the incident surface which may be a surface of the base material layer or the lens layer is totally reflected by the total reflection surface (11a, 23a, 31a, 40a, 50a), when the disoriented light proceeds in a direction from the lens layer side toward the base material side. That is, the disoriented light is originated when the projection light passes through or is reflected back by the surface with the Fresnel lens configuration of the lens layer, and proceeds in a direction from the lens layer side toward the base material side, and thus reaches the total reflection surface, at which the disoriented light is subjected to the total reflection.
In the first aspect, an optical path of the disoriented light in the Fresnel lens sheet is shortened, because the disoriented light is reflected back by the total reflection surface before it proceeds across an entire thickness of the Fresnel lens sheet. Accordingly, an extent of the double image can be reduced, even if thickness of the Fresnel lens sheet is made large to increase the self-standing property, thus providing a Fresnel lens sheet with a good self-standing and a reduced double image.
A first embodiment, which realizes the above-mentioned first aspect of the present invention, provides a Fresnel lens sheet (10, 20, 30) comprising: a base material layer (an incident layer) (12, 22, 32) provided as a layer having an incident surface; a lens layer (11, 21, 31) at which a Fresnel configuration has been formed; and a total reflection surface (11a, 23a, 31a) for totally reflecting a portion of projection light reflected at a light-emission surface (11b, 21b, 31b), wherein the total reflection surface is disposed between the incident surface (12a, 22a, 32a) and the light-emission surface. According to the first embodiment of the present invention, generation of double image can be significantly suppressed, even when the base material is relatively thick. As a result, a Fresnel lens sheet which is easily held and in which double image is not so conspicuous can be obtained.
In the above-mentioned first embodiment, the Fresnel lens sheet (10, 20, 30) may comprise: a low refractive index layer (12, 24, 33) having a predetermined refractive index; and a high refractive index layer (11, 23, 31) having a refractive index higher than the refractive index of the low refractive index layer, the high refractive index layer being adjacent to the light-emission side of the low refractive index layer, wherein the total reflection surface (11a, 23a, 31a) is a surface at which the low refractive index layer is in contact with the high refractive index layer. In this case, as the total reflection surface is a simply boundary surface at which the low refractive index layer is in contact with the high refractive index layer, production of the total reflection surface is significantly eased.
In the Fresnel lens sheet (10) of the above-mentioned first embodiment, the low refractive index layer may be provided as the base material layer (12) and the high refractive index layer may be provided as the lens layer (11). As a result, the present invention can be realized by a simple structure.
In the Fresnel lens sheet (10, 20, 30) of the above-mentioned first embodiment, the distance between the total reflection surface (11a, 23a, 31a) and the light-emission surface (11b, 21b, 31b) is preferably smaller than the distance between the total reflection surface and the incident surface (12a, 22a, 32a). As a result, generation of double image can be suppressed in an effective manner, while the strength of the Fresnel lens is reliably maintained.
In the Fresnel lens sheet (10-2) of the above-mentioned first embodiment, the total reflection surface (11-2a) may have a diffusion configuration constituted of minute projections and dents. As a result, generation of double image can be further suppressed.
In the Fresnel lens sheet (10-3) of the above-mentioned first embodiment, at least one (11-3) of the layers provided between the total reflection surface and the light-emission surface may include a diffusion material (D) which diffuses light. As a result, generation of double image can be further suppressed.
A second embodiment, which realizes the above-mentioned first aspect of the present invention, provides a Fresnel lens sheet (40, 50) comprising: a lens layer (41, 51) which is provided as a layer having an incident surface and at which a Fresnel configuration has been formed; a base material layer (42, 52) provided further toward the light-emission side than the lens layer; and a total reflection surface (40a, 50a) for totally reflecting a portion of projection light incident on the lens layer, the total reflection surface being provided between the incident surface (41a, 51a) and a light-emission surface. As a result, generation of double image can be suppressed regardless of the thickness of the lens layer, whereby a Fresnel lens sheet which is easily held and in which double image is not so conspicuous can be obtained.
In the above-mentioned second embodiment, the Fresnel lens sheet may be designed as a Fresnel lens (40, 50) in which the total reflection surface (40a, 50a) totally reflects a portion of the projection light incident on an ineffective surface (41b, 51b) of the lens layer. As a result, generation of double image can be suppressed regardless of the thickness of the lens layer, whereby a Fresnel lens sheet which is easily held and in which double image is not so conspicuous can be obtained.
In the above-mentioned second embodiment, the Fresnel lens sheet (40, 50) may comprise: a high refractive index layer (41, 51) having a predetermined refractive index; a low refractive index layer (42, 53) having a refractive index lower than the refractive index of the high refractive index layer, the low refractive index layer being adjacent to the light-emission side of the high refractive index layer, wherein the total reflection surface (40a, 50a) is a surface at which the high refractive index layer is in contact with the low refractive index layer. As a result, the total reflection surface can be easily produced.
In the Fresnel lens sheet (40) of the above-mentioned second embodiment, the low refractive index layer may be provided as the base material layer (42) and the high refractive index layer may be provided as the lens layer (41). As a result, the present invention can be realized by a simple structure.
In the Fresnel lens sheet (40, 50) of the above-mentioned second embodiment, the distance between the total reflection surface (40a, 50a) and the incident surface (41a, 51a) is preferably smaller than the distance between the total reflection surface and the light-emission surface. By designing the Fresnel lens sheet in such a manner, generation of double image can be effectively reduced, while the strength of the Fresnel lens is maintained.
In the Fresnel lens sheet (50-2) of the above-mentioned second embodiment, the total reflection surface (50-2a) may have a diffusion configuration constituted of minute projections and dents. As a result, generation of double image can further be reduced.
Further, the second aspect of the present invention provides a transmission-type projection screen provided with a Fresnel lens sheet, wherein the Fresnel lens sheet comprises a base material layer, a lens layer formed into a Fresnel lens configuration, a total reflection surface which is disposed at a position between an incident surface and an light-emission surface and totally reflects a portion of projection light which is incident on the incident surface disposed on either the lens layer side or the base material layer side, and proceeds in a direction from the lens layer toward the base material layer, and finally emitted from the light-emission surface, and wherein the Fresnel lens sheet is further comprises one diffusion means selected from the group consisting of a diffusion material added inside the Fresnel lens sheet, an interface between layers which constitute the Fresnel lens sheet formed into a projection-dent configuration, a light-emission surface formed into a rough face, and a light-emission surface formed into a lenticular configuration.
The above-mentioned transmission-type projection screen can be easily produced by using any of the aforementioned diffusion means.